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Rumen Ammonia Concentration as Influenced by Storage Time, Freezing and Thawing, Acid Preservative, and Method of Ammonia Determination

Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061

ABSTRACT

Twenty-five milliliters of rumen fluid from five cows on a variety of diets were added to either 25 ml .1 N HCl, 5 ml 25% metaphosphoric acid, 5 ml 20% trichloroacetic acid, 5 ml 3 N H₂SO₄, or no preservative. Replicate samples were stored at –20°C until analyzed. One replicate set was analyzed at 7 d, refrozen and analyzed at 35 d, refrozen, thawed, and reanalyzed at 65 d. Another set was thawed and analyzed at 35 d and yet another set kept frozen until analyzed at 65 d. Fresh and frozen samples were quantitated for ammonia by Conway microdiffusion and phenol-hypochlorite reaction.

Ammonia recoveries were 93.8 and 94.1% for the Conway and phenolhypochlorite methods. Storage time and refreezing and thawing had a variable effect on ammonia concentration. Samples with no preservative yielded higher ammonia than those with preservative; ammonia was accentuated by refreezing and thawing up to 65 d. Hydrochloric acid samples had lower ammonia than other acids, especially for the phenolhypochlorite method. Overall, the Conway method resulted in higher ammonia for frozen samples than the phenolhypochlorite method (10.4 vs. 9.0 mg/dl); however, this varied depending on acid.

When rumen fluid samples are to be stored with an acid preservative, .1 N HCl is not recommended. Repeated freezing and thawing of rumen samples used for ammonia analysis should be avoided because of variable results.

¹ Department of Research and Development, Agway Research Center, Tully, NY 13159.

² US Department of Agriculture, Southwestern Livestock and Forage Research Station, P.O. Box 1199, El Reno, OK 73036.